Inner conductor support for shielded microwave strip lines

ABSTRACT

A SHIELD MICROWAVE STRIP LINE HAVING AN INNER CONDUCTOR BETWEEN TWO OUTER CONDUCTORS. THE INNER CONDUCTOR IS MAINTAINED IN A FIXED, SPACED RELATIONSHIP WITH RESPECT TO THE OUTER CONDUCTORS BY A SUPPORTING MEANS WHICH CONNECTS SUCH INNER CONDUCTOR TO ONE OF THE OUTER CONDUCTORS. THE SUPPORTING MEANS IS IN THE FORM OF A DIELECTRIC SCREW WHICH IS INSERTED THROUGH AN OPENING PROVIDED IN THE INNER CONDUCTOR AND A DIELECTRIC SPACER SLEEVE PROVIDED BETWEEN THE INNER AND THE ONE OUTER CONDUCTOR. A METALLIC LOCK NUT IS ALSO PROVIDED WHICH FASTENS THE SCREW IN PLACE. THE SCREW IS FORMED TO OCCUPY ONLY THAT PORTION OF THE INNER CONCONDUCTANCE OF THE SUPPORTING MEANS OVER A WIDE MICROWAVE FREQUENCY BAND. D R A W I N G

R. ESSINGER 3,560,896

Feb. 2', 1971 INNER CONDUCTOR SUPPORT FOR SHIELDED MICROWAVE ST RI-P LINES Filed July 8, 1968 V6 t a. 7 lhw H fl Jnremon- Roland Essinger BY v ATTORNEYS.

United States Patent US. Cl. 333-96 6 Claims ABSTRACT OF THE DISCLOSURE A shield microwave strip line having an inner conductor between two outer conductors. The inner conductor is maintained in a fixed, spaced relationship with respect to the outer conductors by a supporting means which connects such inner conductor to one of the outer conductors. The supporting means is in the form of a dielectric screw which is inserted through an opening provided in the inner conductor and a dielectric spacer sleeve provided between the inner and the one outer conductor. A metallic lock nut is also provided which fastens the screw in place. The screw is formed to occupy only that portion of the inner conductor opening necessary for compensating the transverse conductance of the supporting means over a wide microwave frequency band.

BACKGROUND OF THE INVENTION The present invention relates to shielded microwave strip lines and more particularly to an improved supporting means for the inner conductor of such strip lines.

It is well known in the microwave art to provide shielded strip lines in which an inner conductor of definite thickness is provided where high quality components are required in a given arrangement. A typical shielded microwave strip line includes an inner conductor which is provided between two outer conductors. The inner conductor is maintained at a predetermined distance or spacing from the two outer conductors. The inner conductor is usually provided with a rectangular cross section of particular dimensions. The only dielectric provided in the space between the inner conductor and each outer conductor is air. Therefore, it is necessary, in order to maintain the prescribed impedance characteristics of the arrangement, to provide supporting means between the inner conductor and at least one of the outer conductors, thus to maintain such conductors at a prescribed distance with respect to each other. In fact, it is preferred, that such supporting means be provided between the inner conductor and only one outer conductor, inasmuch as the distance of the second outer conductor from the inner conductor is virtually kept constant by providing external mountingsor supports for the second outer conductor.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved supporting means for the inner conductor of shielded microwave strip lines wherein transverse conductances are compensated over a wide frequency band in the frequency range of microwaves.

In brief, according to the invention, this object is accomplished by providing a supporting means which is constructed in the form of a dielectric screw-type connection. Such a connection includes a dielectric screw which connectingly extends between the inner conductor and one of the outer conductors and passes through an opening provided in such inner conductor and a dielectric spacer sleeve provided between such inner conductor and one ice outer conductor. A metallic lock nut is also provided on the outer surface of the one outer conductor, which fastens the dielectric screw in position. The dielectric screw is formed with respect to the inner conductor opening so that it occupies only such portion of the opening necessary for compensating the transverse conductances of the screw connection over a wide microwave frequency band.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a transverse view of a typical shielded microwave strip line showing a cross section theerof.

FIG. 2 is a side view cross section of the shielded microwave strip line of FIG. 1 showing a supporting means, according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, show therein is an inner conductor 5 which is guided, that is, provided between two outer conductors 6 and 7. The inner conductor 5 is provided at a predetermined position with respect to the two outer conductors and 6 and 7. Thus, a predetermined distance or spacing, h, is provided between the lower surface of the inner conductor 5 and the inner surface of the outer conductor 6. Moreover, the distance, H, provided between the two outer conductors, 6 and 7 respectively, is also predetermined. As shown, the inner conductor 5, preferably, has a rectangular or oblong cross section of a width, b, and a thickness, t. The dielectric provided between the above-mentioned inner and outer conductors is simply air so that it is necessary, in order to maintain the prescribed impedance characteristics of the arrangement, to provide a supporting means at certain intervals along the length of the strip line whereby the position of the inner conductor is maintained constant with respect to the outer conductors.

Referring to FIG. 2, as shown therein, a supporting means for maintaining the distance between the inner and outer conductors constant according to the invention is provided. The shielded microwave strip line includes an inner conductor 5 and two outer conductors 6 and 7, and the dielectric between the conductors is air as discussed above. The supporting means shown in FIG. 2 is provided at regular intervals along the length of the strip line and is in the form of a screw connection. As shown, each screw connection includes a dielectric screw 3 having a head portion 10 and a shaft diameter of D a dielectric spacer sleeve 1, a dielectric sleeve 2 and a metallic nut 8. The inner conductor 5 includes a recess or opening 4 which is aligned with a corresponding recess or opening 9 in the outer conductor 6. The dielectric spacer sleeve 1 is disposed between inner conductor 5 and outer conductor 6. The dielectric screw 3 is inserted through the dielectric sleeve 2, opening 4, dielectric sleeve 1 and the opening 9. The parts 1, 2 and 3 may be formed of commonly known dielectric materials such as polystyrene, polytetrafluor ethylene, polyvinyl carbazole, polymethacrylate or ceramics with low distortions and a small dielectric constant. The metallic nut 8 is then fastened on that portion of dielectric screw 3 which extends beyond the outer surface of outer conductor 6. This arrangement allows the dielectric sleeve 2 to be pressed against the inner conductor 5 and into opening 4 and the dielectric screw 3 itself, to be fixed in position.

As shown, the dielectric sleeve 2 includes two rims of different diameters. The rim of greater diameter, depicted as D corresponds to the diameter of the dielectric sleeve 1, which is preferably equal to the width, b, of the inner conductor 5. This assures a good mechanical compression between the parts of the supporting means. The rim of smaller diameter, depicted as D occupies the opening 4 and is, preferably, equal to about 80 to 90% of the width, b, of inner conductor 5. The rim of greater diameter, D is supported on the surface of the inner conductor 5, while the other rim of the sleeve 2, together with dielectric screw 3, partially occupies the opening 4 in the inner conductor 5. The size of the opening 4 is determined by the amount of interference which must be compensated for by the transverse conductance of the supporting means, which is essentially capacitive. The transverse conductance of the supporting means is compensated over a wide microwave frequency band by the essentially inductive longitudinal conductance of the opening 4. The dielectric materials of the parts 1, 2 and 3 result in a capacitive loading of the strip line, that is to say, an unwanted transverse conductance. The opening 4 essentially acts as a serial inductance. The dimension of opening 4 is appropriately chosen in such-a manner as to obtain compensation of the transverse conductance in a wide frequency band. The effective amount of the opening also depends on the parts 2 and 3.

While not shown in the figures, in a preferred form, according to the present invention, the head 10 of the dielectric screw 3 and the dielectric sleeve 2 are combined into an integrated head unit. In this form, the dielectric sleeve 2 is part of dielectric screw 3.

The following illustration refers to a shielded microwave strip line having an impedance characteristic of 60 ohms. The dimensions of the strip line and supporting means therefore are as follows:

Where a shielded microwave strip line and supporting means of the foregoing dimensions is employed, a dielectric sleeve 2 is provided which has a smaller rim extending 1.4 mm. into the opening 4 of the inner conductor 5 and a'greater rim which extends about 1 mm. above the upper surface of the inner conductor 5. A supporting means arrangement having such dimensions results in a transverse conductance interference factor of less than 1% in the microwave frequency range of up to 2.5 gHz.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations.

What is claimed is:

1. An arrangement for supporting the inner conductor of a shielded microwave strip line comprising, in combination:

(a) an inner conductor having an opening therein;

(b) a pair of spaced outer conductors, said outer conductors being disposed on opposite sides of the inner conductor;

() means disposed between said inner conductor and only one of said outer conductors for supporting the inner conductor in a fixed, spaced relationship with respect to the outer conductors, said means including: (1) a dielectric screw inserted through said inner conductor opening and formed to occupy only such portion of the inner conductor opening necessary for compensating the transverse conductance of the supporting means over a wide microwave frequency band;

(2) a dielectric spacer sleeve disposed between said inner and said one outer conductors and through which said screw is inserted thereby to maintain said inner and said one outer conductors at a fixed, spaced relationship to each other;

(3) said one outer conductor having an opening provided therein and said screw being inserted therein with a portion of the screw extending beyond the outer surface of said outer conductor; and

(4) a metallic lock nut fastened to that portion of the screw extending beyond said outer surface for holding said screw in position. 2. A combination as defined in claim 1 wherein said screw includes a head portion, said head portion and said spacer sleeve being arranged so as to provide a space therebetween.

3. A combination as defined in claim 1 wherein said supporting means includes a dielectric sleeve which partially occupies the inner conductor opening; said screw extending through said sleeve to hold it in position and said sleeve including at least a rim portion which is supported by the surface of said inner conductor adjacent to the inner conductor opening.

4. A combination as defined in claim 3 wherein said supported rim of said additional spacer sleeve has a diameter equal to the long side of the inner conductor oblong cross section.

5. A combination as defined in claim 3 wherein said inner conductor has an oblong cross section two sides of which are longer than the two other sides.

6. A combination as defined in claim 5 wherein the portion of said spacer sleeve, which partially occupies the inner conductor opening has a diameter of about between 45 80 to 90% of the long side of said inner conductor oblong cross section.

References Cited UNITED STATES PATENTS 2,376,725 5/1945 Richardson et a1 333-96 FOREIGN PATENTS 601,514 5/1948 Great Britain 333-84M HERMAN KARL SAALBAOH, Primary Examiner S. CHATMON, 112., Assistant Examiner U.S. c1. xn, 174-77; 333- 4 I 

